Owing to their light weight and excellent shock resistance, synthetic resin containers have been widely used as containers for packing a variety of liquids. Specifically, stretch-formed containers obtained by stretch-blow-forming a polyethylene terephthalate (PET) feature transparency, gas-barrier property, light weight, shock resistance and suitable degree of rigidity in combination, have been widely used as containers for containing liquid contents, and are replacing for the glass bottles that were so far used for containing seasonings and the like contents.
It is a widely accepted practice even for the synthetic resin containers such as of polyesters to be hot-filled with the contents to improve preservation of the contents. The synthetic resin containers, however, are necessarily accompanied by deformation due to a reduction in the pressure since the volume of the content shrinks as it cools down. To prevent this, it has, usually, been attempted to provide the body portion of the container with a panel portion via rib portions so that the panel portion absorbs the deformation caused by a reduction in the pressure (patent document 1, etc.).
However, the contents such as seasonings and the like mentioned above must maintain appearance or images of the traditionally used products by, for example, sticking roll labels onto the glass bottles. Therefore, providing the body portion with the panel portion for reducing or absorbing the pressure is not desirable since it makes it difficult to stick the labels. Besides, the body portion that is irregularly deformed due to a reduction in the pressure can be discerned at a glance. It has, therefore, been desired to provide an art that is capable of coping with a change in the internal pressure without affecting the appearance.
To satisfy the above requirements, there have been proposed a variety of synthetic resin containers provided with the pressure reducing/absorbing capability in the bottom portion thereof without providing the body portion with the pressure reducing/absorbing panel (patent documents 2 and 3).